Algebra Demystified 2nd Ed

290 algebra De mystif ieD

2. The distance between the girls is increasing at the rate of 4 + 6 =
   10 mph. Let t represent the number of hours the girls are walking.

10 3

3

10

t

t

=

=^

Mary and Sharon will be 3 miles apart in 103 of an hour or (^60) () 103  =
18 minutes.

3. The distance between the trains is increasing at the rate of 40 + 60 =
   100 mph. Let t represent the number of hours the trains travel after
   passing each other.
   100 325
   325
   100
   341

t

t

t

=

=

=

The trains will be 325 miles apart after 341 hours or 3 hours 15 minutes.

In the following problems, two bodies leave different locations at the same

time, and they travel in opposite directions (either away from each other or

toward each other). The rate at which the distance between them changes is

the sum of their individual rates.

EXAMPLE

Dale left his high school at 3:45 and walked toward his brother’s school at

5 mph. His brother, Jason, left his elementary school at the same time and

walked toward Dale’s high school at 3 mph. If their schools are 2 miles

apart, when will they meet?

The rate at which the brothers are moving toward each other is 3 + 5 =

8 mph. Let t represent the number of hours the boys walk.

82

2

8

1

4

t

t

t

=

=

=

The boys will meet after^14 an hour or 15 minutes; that is, at 4:00.

EXAMPLE

Dale left his high school at 3:45 and walked toward his brother’s school at